Aspartic Acid 

1.0Introduction

Aspartic acid is an acidic amino acid containing two carboxylic groups and one amino group. Like all amino acids, its structure includes an amino group (–NH₂) and a carboxylic acid group (–COOH). However, what makes aspartic acid unique is the presence of an additional carboxyl group in its side chain, giving it acidic properties.

• Chemical Formula: C₄H₇NO₄
• Common Ionic Form: At physiological pH, the α-amino group is protonated (–NH₃⁺) and the carboxylic groups are deprotonated (–COO⁻).

Aspartic acid is classified as a non-essential amino acid, meaning that the human body can synthesize it as needed.

2.0Aspartic Acid Vs Other Amino Acids

While all amino acids share the common amino and carboxylic functional groups, they differ based on their R-group or side chain. The R-group in aspartic acid contains an extra carboxylic acid, making it negatively charged (anionic) at neutral pH.

• This negatively charged side chain is referred to as aspartate.
• The negative charge allows aspartic acid to participate in ionic interactions, especially in enzyme active sites and protein folding.

Aspartic acid is grouped with acidic, polar amino acids, along with glutamic acid, whose ionized form is called glutamate.

3.0Functions of Aspartic Acid

• Involved in the biosynthesis of other amino acids
• Plays a role in the citric acid cycle (Krebs cycle)
• Participates in the urea cycle, helping to eliminate nitrogen waste
• Acts as a neurotransmitter
• Supports energy production and metabolic regulation

4.0Natural Sources of Aspartic Acid

5.0Structure and Hybridization

Aspartic acid is a dicarboxylic α-amino acid, meaning it contains two carboxyl groups (–COOH) and one amino group (–NH₂). One of the carboxyl groups is connected to the main carbon chain via an additional methylene group (–CH₂–). This structure makes aspartic acid both acidic and polar.

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• Chemical Formula: C₄H₇NO₄
• Molecular Formula: HOOC–CH(NH₂)–CH₂–COOH
• Molecular Weight: 133.1 g/mol
• IUPAC Name: 2-Aminobutanedioic acid
• Isoelectric Point (pI): 2.77, due to the presence of two –COOH groups

The atoms in the aspartic acid molecule exhibit different types of hybridization, which define its shape and bonding:

• Carbon Atoms in Carboxyl Groups (C₁ and C₄):
  Hybridization: sp²
• Geometry: Trigonal planar, bond angles ≈ 120°
• Alpha and Beta Carbon (C₂ and C₃):
  Hybridization: sp³
• Geometry: Tetrahedral, bond angles ≈ 109.5°
• Nitrogen Atom in the Amino Group:
  Hybridization: sp³
  Bonds to: One carbon and two hydrogen atoms

6.0Properties of Aspartic Acid

• The presence of a second carboxylic acid group makes aspartic acid highly hydrophilic.
• Its side-chain carboxyl group has a pKa of 3.85, allowing it to readily form ionic bonds with metal ions and engage in dipole interactions with water.
• Aspartic acid typically carries a negative charge at physiological pH, and thus is commonly located on the surface of proteins, where it can interact with aqueous environments.

Physical Properties of Aspartic Acid

Aspartic acid, a non-essential amino acid, exhibits the following physical characteristics:

• Density: 1.7 g/cm³
• IUPAC Name: (2S)-2-aminobutanedioic acid
• Molecular Formula: C₄H₇NO₄
• Molecular Weight: 133.103 g/mol
• Appearance: Colourless crystalline powder
• Solubility: Soluble in water
• Melting Point: 270°C ( 518°F)
• Boiling Point: 324°C ( 615°F)
• Magnetic Susceptibility: –6.42 × 10⁻⁶ cm³/mol
• Charge: Negatively charged at physiological pH

pKa Values of Functional Groups in Aspartic Acid:

7.0Types of Aspartic Acid (Enantiomers)

Aspartic acid exists as two enantiomers:

1. L-Aspartic Acid
   Naturally occurring and directly incorporated into proteins during translation.
2. D-Aspartic Acid
   Found in limited quantities in mammalian tissues and certain microorganisms.
   Involved in specific biological processes, including hormone regulation and neurotransmission.

These enantiomers are mirror images of each other, and while structurally similar, their biological roles differ significantly.

8.0Uses of Aspartic Acid

Aspartic acid is useful in a variety of industrial and biological applications:

1. Pharmaceutical Industry:
   Used in medicines to support amino acid metabolism and nerve health.
2. Biodegradable Polymers:
   Forms polyaspartic acid, a sustainable alternative to polyacrylates used in superabsorbent materials.
3. Artificial Sweeteners:
   Acts as a key ingredient in low-calorie sweeteners, suitable for diabetic patients.
4. Corrosion Inhibitors and Resins:
   Used in the manufacture of environmentally friendly corrosion-resistant coatings and industrial resins.
5. Agriculture and Fertilizers:
   Enhances soil nitrogen absorption and moisture retention, aiding plant growth and crop yield.